The hemodynamic responses of postmenopausal women to passive heat stress have not been characterized to date. This proposal outlines two studies which seek to characterize postmenopausal women's hemodynamic responses to passive heating through an investigation of the separate roles of hormone replacement therapy and hydration. It is the purpose of the second investigation in this proposal to examine the role of hydration on postmenopausal women's responses to passive heating. It is hypothesized that: 1) hydration will increase cardiac output; and 2) hydration with a commercially available sports drink will be better than hydration with water.